Method and apparatus for cutting devices from conductive substrates secured during cutting by vacuum pressure

ABSTRACT

A method and system for cutting a wafer comprising a conductive substrate attached to an array of integrated devices includes placing the wafer on a stage such as a movable X-Y stage including a vacuum chuck having a porous mounting surface, and securing the wafer during and after cutting by vacuum pressure through the pores. The wafer is cut by directing UV pulses of laser energy at the conductive substrate using a solid-state laser. An adhesive membrane can be attached to the separated die to remove them from the mounting surface, or the die can otherwise be removed after cutting from the wafer.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/288,719,filed 5 Nov. 2002 now U.S. Pat. No. 6,806,544.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and processes used inmanufacturing integrated device die, such as integrated circuits andlaser diodes, including diode lasers formed on conductive substrates.More particularly, the present invention provides for securing wafershaving conductive substrates, during the process of cutting the wafersinto individual die, and further provides for securing the die separatedfrom the wafers during and after the wafer cutting process.

2. Description of Related Art

Sapphire Al₂O₃ is used as a substrate for the growth of Gallium NitrideGaN in commercial laser diode manufacturing systems, and can also act asthe substrate of the finished product. However, the use of sapphiresubstrates introduces certain problems.

For instance, sapphire is an electrical insulator and this causesproblems when it is used as a wafer substrate in the fabrication oflaser diodes. Because it is an insulator, electrical contacts to thediodes are usually placed on the wafer's active surface, and thesecontacts occupy areas that would otherwise be utilized for generationand emission of light.

Efforts have been made to implement laser diodes using GaN with othersubstrates. These approaches typically involve removal of the GaN fromthe sapphire substrate on which it is grown, and then remounting it onanother substrate. Advantages of this approach arise because copper orother metal substrates are excellent heat and electric conductionmaterials. A light emitting diode or laser diode LED with a metalsubstrate can be driven with higher current and yield brighter output.In addition, the device with good electric conduction to the substraterequires only one wire bonding on the active surface, and yields higheroutput. Furthermore, the sapphire substrate used for growth of the GaNmay be reused for reduced cost.

For example, U.S. Pat. No. 6,365,429 teaches a method by which “removalof the sapphire substrate after growth of the laser diode arraystructures simplifies providing electrical contacts to the laser diodearrays and avoids special architectures while allowing a superior heatsink to be attached to the laser diode arrays. The laser diode array maybe attached to a thermally conductive wafer before or after substrateremoval by soldering, thermo-compression bonding or other means.” (col.2 11. 20–28)

However, no known method or tools to dice this type of wafer have beenapplied on a commercial scale.

Present methods of separating a wafer based on a sapphire or crystallinesemiconductor substrate into die involve scribing the wafer after firstadhering the wafer to a flexible sheet, known as “blue tape”. Afterscribing, mechanical pressure is applied to break the wafer along thescribe lines, leaving the die attached to the flexible sheet for theirsubsequent removal.

However, wafers having metal substrates cannot be separated into dieusing scribing techniques. Rather, wafers having a metallic substrate,for example one made of copper, must be cut completely through to obtainseparated die. Cutting completely through the wafer would damage anadhesive sheet attached to the wafer, unless very precise control of thecutting process were possible. Furthermore, if an adhesive sheet is notattached to the wafer prior to cutting the die, in order to avoid thedamage, the separated die would be difficult to handle during and afterthe cutting of the wafer. Thus, there is a need for a method and systemfor securing both the wafer and the separated die during and after thecutting of the wafer.

It is desirable, therefore, to provide a system and method for dicingwafers having conductive or metallic substrates, for use in fabricatingdie in large volume, in an efficient manner that maximizes thedie-manufacturing yield. Furthermore, it is desirable that such a systembe compact, safe to operate, and low cost.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide forsecuring a substrate to a mounting surface in order to perform thecutting substantially through the substrate, thereby permittingseparation of the substrate into die in accordance with a cuttingpattern. It is a further object of the present invention to provide forsecuring the separated die to the mounting surface, both during andafter the cutting process.

One embodiment of the invention provides a method for dicing a wafer,comprising mounting the wafer on a porous member having a mountingsurface; securing the wafer on the mounting surface by applying suctionto the wafer through pores in the porous member; and dicing the waferinto individual die, the die remaining secured to the mounting surfaceby the applied suction.

The present invention provides a method comprising mounting a waferhaving substrate, and carrying an array of integrated devices, on astage such as a movable X-Y stage further comprising a vacuum chuckprovided with a porous mounting surface. Applying suction through thepores of the mounting surface secures the wafer to the mounting surface.The wafer is cut in one embodiment by directing laser energy at asurface of the wafer using a solid-state laser, to form a plurality ofkerfs substantially through the thickness of the wafer, thereby dicingthe wafer. Cutting a wafer by the present method cuts kerfs through thewafer, the kerfs having a width preferably in the range of 10 to 20microns.

The present invention is suitable for manufacturing blue laser diodesbased on Gallium Nitride structures that have been removed from thesubstrate on which they were grown, and then mounted on a conductivesubstrate. According to the present invention, greater device density onthe wafer, and greater manufacturing yield are achieved, while alsoreducing the time required for dicing the wafer into individual die.Furthermore, the present invention is based on compact, low-costmachines, and otherwise reduces the overall manufacturing costs for suchintegrated device die.

In accordance with the present invention, the X-Y stage comprises avacuum chuck provided with a thin porous mounting surface. The porousmounting surface in various embodiments comprises a thin paper, plastic,ceramic or metal disk having dense micro pores through which a negativepressure can be applied to a wafer placed in direct contact with themounting surface. Embodiments of the porous member comprise one or moreof porous paper, gas filters, sintered ceramic disks or plates, andsintered metal disks and plates made of various compositions.

Also in accordance with embodiments of the present invention, themounting surface comprises a removable member. The use of a removablemember further permits the ready replacement of the mounting surfacewhen required due to wear or contamination.

The laser energy utilized in some embodiments to cut kerfs in the wafershould have a wavelength highly absorbed in the material of thesubstrate. Further, the wavelength should be selected so that it isabsorbed to a much greater degree in the substrate than in the porousmember, so that when the substrate is cut through and the laser impactsthe porous member, minimal damage is caused to the porous member. Forcopper and similar metal substrates, the wavelength is preferably belowabout 560 nanometers, and more preferably between about 150 in 560nanometers. In addition, energy density, spot size, and pulse durationare established at levels sufficient to cut kerfs completely through thewafer. Control of the system, such as by moving the stage whilemaintaining a stationary beam path for the pulses, causes the pulses tocontact the conductive substrate in a cutting pattern at a rate ofmotion causing overlap of successive pulses sufficient to cut throughthe conductive substrate and other portions of the wafer.

Embodiments of the present invention utilize laser pulses having anenergy density between about 10 and 100 joules per square centimeter, apulse duration between about 10 and 30 nanoseconds, and a spot sizebetween about 5 and 25 microns. The repetition rate for the pulses isgreater than 5 kHz, and preferably ranges from about 10 kHz to 50 kHz orhigher. The stage is moved at a rate of motion causing overlap of thepulses in the amount of 50 to 99 percent. By controlling the pulse rate,the rate of motion of the stage, and the energy density, the depth ofthe cut can be precisely controlled, to provide for cutting through thewafer while minimizing the amount of laser energy reaching the mountingsurface securing the wafer.

In embodiments of the present invention, the solid-state laser comprisesa diode pumped, Q-switched, Nd:YVO₄ laser, including harmonic frequencygenerators such as nonlinear crystals like LBO, so that output of thelaser is provided at one of the second, third, fourth and fifth harmonicfrequencies of the 1064 nanometer line produced by the neodymium doped,solid-state laser. In particular systems, the third harmonic frequencyof about 355 nanometers is provided. In other embodiments, thesolid-state laser comprises a Q-switched, Nd:YAG laser, operating toprovide one of the harmonic frequencies as output.

In embodiments of the invention, the method includes detecting edges ofthe conductive substrate while directing pulses at the substrate in thecutting pattern. In response to detected edges, the system prevents thepulses of radiation from being directed beyond the substrate.

Embodiments of the present invention direct the pulses of laserradiation at the backside of the wafer substrate.

Thus, embodiments of the invention include mounting the wafer on thestage, moving the wafer under conditions causing cutting of theconductive substrate in a cutting pattern on the backside of thesubstrate, and detecting edges of the substrate during the cuttingprocess to prevent the pulses of laser radiation from impacting themounting surface.

The die defined by a cutting pattern are separated from the wafer by thelaser energy, while the suction applied through the pores of themounting surface continues to secure them substantially in the samelocation they occupied on the mounting surface prior to the cutting. Inone embodiment, an adhesive tape is placed onto the separated die afterdicing the wafer is completed, in order to permit removal of the die asa set, and facilitate their handling for subsequent manufacturing steps.Furthermore, the die separated from the wafer remain adhered to theadhesive tape until removed using a pick and place robot, or othertechnology.

Certain embodiments of the invention further provide for controllingpolarization of the laser pulses with respect to direction of the kerfsin the cutting pattern. The polarization is controlled so that kerfs aremore uniform for kerfs cut parallel to different axes. Uniformity can beimproved by random or circular polarization of the pulses in someembodiments. More preferably, polarization of the pulses is controlledso that the polarization is linear and parallel to the kerfs being cut.Embodiments of the invention provide for control of the polarizationusing a laser with an adjustable polarizer, such as a half wave plate,in the optical path.

The invention also provides a system for cutting wafers having aconductive substrate which comprises a solid-state laser, as describedabove, a stage having a vacuum chuck with a porous surface adapted tosupport and move a conductive substrate, optics directing pulses toimpact of conductive substrate mounted on the stage, an edge detectionsystem which detects edges of substrate mounted on the stage duringmovement of the stage, and a control system. The control system inembodiments of the invention comprises a computer system coupled to thesolid-state laser, the stage, and the edge detection system. Thecomputer is responsive to the edge detection system and parameters setby users to cause the pulses to impact of the conductive substrate in acutting pattern at a rate of motion causing overlap of successive pulsessufficient to cut kerfs in the conductive substrate. Embodiments of theinvention also include a debris exhaust system coupled with the stage.

Embodiments of the invention include a user interface with logic to setup the cutting pattern, and the operational parameters including pulserepetition rate, stage velocity and energy levels to establish kerfdepth, cutting speed and other characteristics of the process.

Other aspects and advantages of the present invention can be seen onreview of the drawings, the detailed description, and the claims whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a wafer cutting system accordingto the present invention.

FIG. 2 is a perspective view of a compact, portable wafer cutting systemaccording to one embodiment of the present invention.

FIG. 3 is a simplified block diagram including the laser system andoptics for the wafer cutting system of the present invention.

FIG. 4 is a simplified block diagram of the edge detection according toone embodiment of the present invention.

FIG. 5 is a perspective view of the X-Y stage comprising a vacuum chuckhaving a porous mounting surface, and a debris exhaust system, of thewafer cutting system according to one embodiment of the presentinvention.

FIG. 6 is an image of a kerf on a conductive substrate including anarray of integrated laser diodes according to the present invention.

FIG. 7 is a perspective view of a wafer, the porous member, and thevacuum chuck employed in the wafer cutting system of the presentinvention.

FIG. 8 is a top view of a wafer showing a representative cuttingpattern.

FIG. 9 illustrates a process of applying adhesive flexible tape to thecut wafer, in accordance with one embodiment of the present invention.

FIG. 10 illustrates the array of elements adhered to the adhesive tapeafter removal from the stage of the cutting system.

FIG. 11 is a basic flow chart of a manufacturing method according to thepresent invention.

DETAILED DESCRIPTION

A detailed description of embodiments of the present invention isprovided with reference to FIGS. 1 through 11.

FIG. 1 is a simplified block diagram of a wafer cutting system accordingto the present invention. In the embodiment shown, wafer 14, including aconductive substrate and an active layer, is mounted with its activesurface facing downward on movable X-Y stage 15. The stage 15 includes aporous member 25 on which the wafer is secured by suction through poreson the surface of the porous member. High-intensity UV laser energy isdirected at the conductive substrate surface of the wafer through UVobjective 13. A diode pumped, solid-state laser 10 generates thehigh-intensity UV and close-to-UV pulses at a repetition rate in the kHzrange. In preferred systems, the laser comprises a Q-switched Nd:YVO₄medium delivering third harmonic output as the stream of laser pulses ata repetition rate greater than 10 kHz, with a pulse duration of about 40nanoseconds. The pulses are provided using an optical delivery system 11and turning mirror 12 to an ultraviolet objective lens 13, which focusesthe pulses on wafer 14.

The wafer 14 is supported on a vacuum chuck on X-Y stage 15. In theembodiment shown, the wafer is supported with its active surface down ona porous member 25 having a mounting surface. A vacuum system appliessuction to wafer 14 through the pores of the mounting surface, therebysecurely holding the wafer to the vacuum chuck while the X-Y stage ismoved beneath the UV objective, to cut the wafer using laser energy, inaccordance with the cutting pattern. A gas debris removing system 16cooperates with a gas exhaust system and vacuum 17 to remove debrisgenerated by the ablation of the conductive substrate and wafermaterials.

FIG. 2 is a perspective view of a wafer cutting system in one embodimentof the invention. The X-Y stage 15 and porous member 25 are locatedbeneath microscope 52. The diode pumped solid-state laser is compact andlow-cost so that it is efficiently mounted on a cart as illustrated. Thecomputer and other system electronics are contained on the cart. Thecomputer keyboard 50 is mounted on a keyboard tray, which slides in andout of the cart. A flat-panel display 51 is mounted on a swivel base, sothat it may be folded in during movement and storage of the cart. Thesystem includes a microscope 52, which enables viewing of the waferduring the cutting process. Microscope 52 also serves to deliver thelaser energy used in cutting the wafer. Images generated by the camera22, and graphical user interface tools and other display constructs arepresented to the user using the display 51.

The X/Y stage includes a vacuum chuck having a porous member providing amounting surface at least 2.5 inches in diameter, on a six-inchplatform, for holding a two-inch wafer during alignment and cutting. Theporous member is removable in some embodiments of the invention.Representative vacuum chucks that are adaptable for use in the presentinvention are described in U.S. Pat. No. 4,906,011, entitled VACUUMCHUCK.

In one embodiment, the wafer holding surface of the porous member ismade of sintered ceramic materials. For representative examples of thesesintered ceramic mounting members, the wafer mounting or holding surfacehas pore sizes in a range between 0.15 um and 10 um, with a porosityrange between 25% and 75% by volume.

In other embodiments of the present invention, the wafer holding surfaceof the porous member is made of sintered metallic materials. Forrepresentative examples of these sintered metallic mounting members, thewafer mounting or holding surface has pore sizes in a range between 1 umand 20 um, with a porosity range between 10% and 60% by volume.

In yet other embodiments of the present invention, the wafer holdingsurface of the porous member is made of flexible porous materials, suchas paper or plastic. For these flexible porous mounting members, thepore distribution varies in accordance with the type of porous materialutilized. In some embodiments of the invention, the porous member isdisposable and can be removed and replaced between wafers during thecutting process, at low cost. In one example embodiment, the porousmember comprises a leaf of commercially available lens paper, typicallyused for cleaning optical lenses.

Generally, embodiments of the present invention are provided as asemi-automatic turnkey system using a tabletop laser system and computermounted on a cart. The system provides for manual loading and unloadingof wafers. However, the invention contemplates automated wafer loadingand unloading systems as well. Representative systems are adapted toreceive two inch conductive substrate wafers with die sizes, for exampleabout of 250 to 300 square. Smaller and larger die sizes are readilyhandled. The wafer thickness ranges from about 80 to 200 microns, fortypical laser diode die. The wafer is manually placed on the stage andsecured using the suction of the vacuum chuck. Manual alignment of thewafer is possible using manual stage controls. Software controlledcutting patterns are implemented with computer control of the waferstage, and controllable speed in the X- and Y-directions. The systemincludes a class one laser system which generates spot sizes less than20 microns in operational conditions. A kerf is cut to a depth close tothe thickness of the wafer, and more preferably equal to the thicknessof the wafer. Nitrogen gas is used by the debris removing jet, andevacuated using an exhaust pump. Minimal or no damage is caused to themounting surface because the wavelength of the laser is selected so thatit is not significantly absorbed by the porous member, and because ofthe edge detection process, supporting greater yield in the wafercutting process.

The laser system in a preferred embodiment is an electro-opticallyQ-switched, diode pumped, third harmonic Nd:YVO₄ providing an output at355 nanometers wavelength. The is pulses have a TEM₀₀ intensity profilewith 10 to 15 micron, or smaller, diameter at 1/e² peak magnitude spotsize on the target surface. The laser pulse duration is about 40nanoseconds, or less and more preferably between about 30 and 10nanoseconds, for example about 16 nanoseconds.

The basic structure of the laser system is like the commerciallyavailable Acculase SS10 Laser System, by New Wave Research, of Fremont,Calif., which is the assignee of the present invention.

The computer system allows for automated control of the laser and stagemovement for defined cutting patterns, which can be set up using thecomputer. A wafer map and cutting definition function allows setup ofthe cutting pattern including rotation control of the stage. Videooverlay shows live video of the sample within a software-controlledwindow to facilitate set up and monitoring of the process. Control forthe cutting parameters including laser energy, repetition rate and stagespeed are provided via the user interface, giving the operator precisecontrol over the depth and quality of the scribing process. A patternalignment function allows the cutting pattern to be moved in the X-, Y-and orthogonal directions to match the actual wafer location duringsetup.

FIG. 3 is a basic layout of optical path for one embodiment of thecutting system according to the present intention. The optical pathincludes a laser 50, optics delivering the output of the laser to asubstrate 74 mounted on the mounting surface of porous member 78 on thevacuum chuck 75 mounted on an X-stage 76 and Y-stage 77. The porousmember 78 in this embodiment is attached to the vacuum chuck 75. Inother embodiments, the porous member 78 is secured to the vacuum chuckby suction during operation.

The laser includes a resonant cavity defined by high reflector 51 andoutput coupler 59. A beam expander 52, laser medium rod 53, cylindricallens 54, diode array 55, thin film polarizer 56, thin film polarizer 57,and electro-optic Q-switch 58 are included. The diode array is operatedto pump the rod 53 to induce resonance at the 1064 nm line for Nd:YVO₄.The output beam is directed to turning mirror 60 and turning mirror 61through spherical focal lens 62 through nonlinear crystal 63. Thenonlinear crystal 63 produces a second harmonic and passes the secondharmonic along with the primary line through spherical focal lens 64 toa second nonlinear crystal 65. The second nonlinear crystal produces athird harmonic output, among others, which is delivered to turningmirror/filter 66 and turning mirror/filter 67 and half lambda wave plate68. The wave plate 68 is motorized and acts as a controllable polarizerfor the output beam. The wave plate 68 may be used to align thepolarization of the output beam with respect to the cutting direction tomake a kerfs cut by the laser pulses uniform in the X- and Y-directions.The third harmonic output, at a wavelength of about 355 nanometers, isdelivered to optics including turning mirror 69, beam expander 70,turning mirror 71, turning mirror 72 and objective 73 to the conductivesubstrate 74. The objective lens 73 is a 20× lens in this embodiment.

The nonlinear crystal 63 used for second harmonic generation can be madeof a variety of materials, preferably LBO, BBO or KTP. Likewise, thenonlinear crystal 65 used for third or higher harmonic generation can bemade of a plurality of materials, preferably LBO or BBO. In onepreferred system, LBO is utilized for both nonlinear crystals 63 and 65.

FIG. 4 illustrates the edge detection system used in preferredembodiments of the present invention. The system includes a white lightsource 81 which provides light through turning mirror 82 and objectivelens 84 to the conductive substrate 85 on the porous surface 86 of amounting medium. Reflected light passes through objective lens 84,turning mirror 83, turning mirror 82 and is deflected by turning mirror87 through a spherical focal lens 88 to a photodetector 89. Thephotodetector 89 is coupled with the computer system, and its outputindicates edge detection. The edge of the wafer is detected based on thesignificant difference of light contrast between the wafer surface 85and the holding surface on which the wafer is mounted. The computersystem stops the motion of the stage upon receipt of the edge detectionsignal, preventing laser pulses from being directed beyond the surfaceof the wafer.

FIG. 5 provides a perspective of the stage 100, objective lens 101 anddebris removal jet 102 in one embodiment of the invention. The stage 100includes a vacuum chuck 103 centered on a movable plate 104. The vacuumchuck further comprises porous member 106, having a mounting surface forholding the wafer. A movable plate 104 includes manual adjustment knob105 for the Y-direction and a similar adjustment knob (not shown) forthe X-direction. Also, the movement of the stage is automaticallycontrollable. The jet 102 is arranged to deliver air or nitrogen gasinto the region of the ablation in order to remove debris. A vacuum (notshown) withdraws the gas with the debris from the region of the wafer.

In a representative system, the repetition rate is controllable within arange of 20 to 50 kHz, with a stage speed ranging up to 8 to 10 mm persecond. Other combinations of repetition rate and stage speed will bedeveloped according to the needs of a particular implementation.

FIG. 6 shows a magnified view of a wafer having an array of laser diodesformed thereon. Spaces, or streets, about 35 microns wide are leftbetween the individual laser diodes to allow room for cutting. In FIG.6, kerfs (dark lines within the streets) are machined having a width of10–15 microns, on the top surface for perspective of the relativewidths. In a preferred system, kerfs are cut through from the backsideof the wafer. With the system of the present invention with a spot sizein the range of 10 microns, and the precision available, the streets canbe reduced to 20 or 30 microns in width or less. This significantlyincreases the density of devices that can be made on a single substrateand improves throughput in manufacturing process for the die.

FIG. 7 illustrates the basic process of the present convention. Inparticular, a porous member 202 is secured to a vacuum chuck 203. Thevacuum chuck is coupled via coupling 204 to a source of vacuum suction.The porous member 202 may be secured to the vacuum chuck 203 by thesuction of the vacuum, or may be more securely attached depending on theneeds of the particular implementation. A wafer 201 is placed on theporous member 202, and secured on the porous member by suction throughthe pores in the surface of the porous member during the cuttingoperation. Laser pulses 200 are directed at the wafer 201 for thepurposes of cutting kerfs through the wafer. The wafer 201 comprises alayer of GaN 5 to 10 microns thick and a metal substrate such as copperabout 100 microns thick.

FIG. 8 illustrates a cutting pattern for the kerfs. As can be seen,horizontal kerfs 211 and vertical kerfs 210 are cut in the wafer toseparate individual elements from the wafer. For a typical GaN laserdiode, the elements are rectangles or squares about 250 to 300 micronson a side. Each individual element will include one or more laser diodesin the various embodiment of the invention. Shapes other than square orrectangular may be made as well.

As shown in FIG. 9, the wafer 201 has been secured on the porous member202 by suction supplied by the vacuum chuck 203 and the source of vacuum204. Laser pulses have been applied to cut the wafer 201 into an arrayof individual elements. A flexible adhesive tape 221, known as “bluetape” in the semiconductor manufacturing industry, is applied to a frame220. The frame 220 with the tape 221 is lowered onto the array ofelements which had been cut from the wafer 201. The array of elementsadheres to the adhesive tape 221, the vacuum is reduced or removed, andthe adhesive tape 221, attached to the frame 220 with the array ofelements adhered thereto, are removed from the workstation.

FIG. 10 illustrates a resulting workpiece including the frame 220, withthe flexible tape 221 having an array of individual elements, such aselement 222, adhered thereto. The workpiece of FIG. 10 is then suppliedto a pick and place robot system, where the adhesive tape is stretchedto separate the individual elements, and robot may remove the elementsfor further processing.

The basic manufacturing process is shown in the flowchart of FIG. 11. Asmentioned above, the present invention is particularly applicable tomanufacturing of blue laser diodes based on gallium nitride. The galliumnitride is first grown on a sapphire substrate according to thetechnology known in the art. A layer of gallium nitride is removed fromthe sapphire substrate, and attached to a copper or aluminum substrate,or another conductive substrate. The resulting wafer including thecomposite of gallium nitride and a conductive substrate, is placed on aporous surface of a vacuum chuck in a first step of the cutting process(block 300). In a next step, suction is applied to secure the wafer onthe porous surface (block 301). The wafer is cut into an array ofelements, using a laser or other cutting technique (block 302). Aflexible adhesive tape is applied to the array of elements (block 303).The tape is removed with the array of elements adhering thereto, fromthe workstation (block 304). A robot is then used to remove the elementsfrom the tape (block 305). In alternative embodiments, the elements areremoved from the porous surface using a robot, or otherwise, withoutadhesive tape.

The present invention provides a process for manufacturing laser diodedie, and other integrated device die, formed on conductive substrates.Procedures according to embodiments of the invention include thefollowing:

-   -   1) laying out and forming laser diodes in an array on an active        surface of a sapphire substrate, with individual laser diodes        separated by streets having a width less than 40 microns, and        preferably around 25 microns or less;    -   2) removing the sapphire substrate of the wafer from the active        surface having the array of laser diodes;    -   3) attaching an electrically conductive substrate on the wafer,        on the underside of the active surface having the array of laser        diodes;    -   4) placing the wafer having a conductive substrate with the        active surface facing down on the porous mounting surface of the        X-Y stage;    -   5) moving the wafer to a home position by controlling the stage    -   6) automatically, or semi-automatically, aligning the wafer        position to coordinates established by the computer setup;    -   7) setting up a cutting pattern based on wafer and die size and        layout parameters;    -   8) automatically, or semi-automatically, setting up the lighting        levels for edge detection;    -   9) setting up stage speed, laser polarization and laser power        for the required cutting depth;    -   8) turning on the debris removing system;    -   9) starting the process of laser cutting based on the cutting        pattern on one line parallel to one axis;    -   10) continuing the process on other lines and axes, while        controlling polarization, until cutting of the wafer is        finished;    -   11) causing the stage to return to an exit position;    -   12) attaching a wafer tape on a metal frame to the cut wafer,        turn off the vacuum, and removing the cut wafer from the chuck;    -   13) cleaning wafer with high-speed air or other gas jet to        remove laser machining induced debris;    -   14) stretch the wafer tape for separation of the die, for their        transport to other mounting apparatus using a pick and place        system.

The procedures outlined above are carried out using the systemsdescribed above, or similar systems.

Accordingly, the present invention provides a significantly improvedwafer cutting process and system for use-with conductive substrates. Theprocess and system are low-cost, high yield, and high throughputcompared to prior art conductive substrate cutting technologies.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations willreadily occur to those skilled in the art, which modifications andcombinations will be within the spirit of the invention and the scope ofthe following claims.

1. A method for cutting a workpiece, comprising: placing the workpieceon a porous member having a mounting surface; securing the workpiece onthe mounting surface by applying suction to the workpiece through poresin the porous member; using laser energy to cut through the workpiece,and separate the workpiece into individual elements without cracking,the elements remaining secured to the mounting surface by the appliedsuction.
 2. The method of claim 1, wherein the laser energy has awavelength that is absorbed to a greater degree by the workpiece than bythe mounting surface.
 3. The method of claim 1, further comprising:reducing the suction to release the elements from the mounting surface;and removing the elements from the mounting surface.
 4. The method ofclaim 1, further comprising; after said cutting the workpiece, adheringthe elements to a flexible sheet; and removing the elements adhered tothe flexible sheet from the mounting surface.
 5. The method of claim 1,further comprising: after said cutting the workpiece, using a roboticdevice to remove the elements from the mounting surface.
 6. The methodof claim 1, wherein the porous member comprises a rigid plate.
 7. Themethod of claim 1, wherein the porous member comprises a flexible sheet.8. The method of claim 1, wherein the porous member comprises paper. 9.The method of claim 1, wherein the porous member comprises plastic. 10.The method of claim 1, wherein the porous member comprises ceramic. 11.The method of claim 1, wherein the porous member comprises metal. 12.The method of claim 1, wherein the workpiece comprises a wafer having anactive surface, and the active surface is mounted in contact with themounting surface.
 13. The method of claim 1, wherein the workpiececomprises an array of integrated devices on a wafer having an activesurface and comprising a conductive substrate.
 14. The method of claim1, wherein the workpiece comprises a wafer having an active surfacecomprising GaN, and a metallic substrate.
 15. The method of claim 1,wherein the workpiece comprises an array of integrated devices.
 16. Themethod of claim 1, wherein the workpiece comprises a wafer having anactive surface and a back surface, and the back surface is mounted incontact with the mounting surface.
 17. A method for cutting a workpiece,comprising: placing the workpiece on a porous member having a mountingsurface, wherein the workpiece comprises an array of devices on a metalsubstrate; securing the workpiece on the mounting surface by applyingsuction to the workpiece through pores in the porous member; using laserenergy to cut through the metal substrate of workpiece, and separate theworkpiece into individual elements, the elements remaining secured tothe mounting surface by the applied suction.
 18. The method of claim 17,wherein the laser energy has a wavelength that is absorbed to a greaterdegree by the metal substrate of the workpiece than by the mountingsurface.
 19. The method of claim 17, further comprising: reducing thesuction to release the elements from the mounting surface; and removingthe elements from the mounting surface.
 20. The method of claim 17,further comprising; after said cutting the workpiece, adhering theelements to a flexible sheet; and removing the elements adhered to theflexible sheet from the mounting surface.
 21. The method of claim 17,further comprising: after said cutting the workpiece, using a roboticdevice to remove the elements from the mounting surface.
 22. The methodof claim 17, wherein the porous member comprises a rigid plate.
 23. Themethod of claim 17, wherein the porous member comprises a flexiblesheet.
 24. The method of claim 17, wherein the porous member comprisespaper.
 25. The method of claim 17, wherein the porous member comprisesplastic.
 26. The method of claim 17, wherein the porous member comprisesceramic.
 27. The method of claim 17, wherein the porous member comprisesmetal.
 28. The method of claim 17, wherein the workpiece comprises awafer having an active surface, and the active surface is mounted incontact with the mounting surface.
 29. The method of claim 17, whereinthe devices comprises GaN based devices.
 30. The method of claim 17,wherein metal substrate is mounted in contact with the mounting surface.